Project Summary One of the most challenging problems facing society is the mixed benefit of longer lifespan that is also accompanied by the increased risk for neurodegenerative diseases. A central theme of this proposal is that aging is associated with the declining capability of the protein quality control machinery, leading to protein misfolding and aggregation, and resulting in cell and tissue failure and neurodegenerative disease. In this PPG, we have assembled the team of S. Finkbeiner (UCSF), D. Finley (Harvard), J. Frydman (Stanford), J. Kelly (Scripps) and R. Morimoto (Northwestern) to examine proteostasis failure in aging as the basis for misfolding and aggregation of Tau, SOD1 and expanded polyQ in Alzheimer's disease (AD), ALS, Huntington's disease and Ataxias, respectively. A distinctive strength of this PPG team is our expertise with multiple biological systems including S. cerevisiae, C. elegans, mice, patient derived cells and differentiated neurons, and multiple experimental approaches from biochemical and biophysical, live cellular imaging of aggregation phenotypes, and small molecule high-throughput screens. We posit that the unique richness of approaches afforded by this team will provide novel insights that will uncover how aging affects the proteostasis network (PN) of protein synthesis and molecular chaperones, transport machineries, and the degradative arms of the PN comprised of the ubiquitin-proteasome and autophagy lysosomal pathways. An understanding of how aging affects the PN at the cellular, tissue, and organismal level will provide a mechanistic understanding on the events during proteostasis failure that contributes to and accelerates aggregation of Tau, SOD1 and expanded polyQ proteins leading to AD and other neurodegenerative diseases. Through four Projects and four Cores, our team will explore how aging affects the function of molecular chaperones to influence nascent- chain synthesis and the off-pathway aggregation properties of Tau and polyglutamine in yeast (Proj. 1) and in different tissues of short-and-long-lived C. elegans (Proj. 4). We will examine the degradative arms of the PN in transgenic mice with altered levels of proteasome activity and the effects on proteotoxicity of Tau and mutant SOD1 (Proj. 2), and in human iPSCs derived patient neurons by monitoring the autophagic lysosomal pathways (Proj. 3) challenged by aging and expression of Tau or TDP43. These Projects will be supported by: the coordinating Administrative Core A, Proteostasis Sensors Core B that develops PN reporters to quantify different PN activities, Proteostasis Proteomics Core C, and the Proteostasis Regulator Pharmacology Core D to develop a small molecule strategy to restore PN functionality in aging and neurodegenerative disease. Working together, the Cores and Projects will generate PN reagents and tools, datasets and small molecules to quantify and perturb different components of the PN, to generate a comparative analysis of aging and neurodegeneration across all biological systems, and to develop a small molecule strategy to prevent or reverse the age-and-disease dependent failures in the PN leading to neurodegenerative disease.